In a film-forming step for manufacturing semiconductor devices, there is used, for example, a sputtering apparatus. The sputtering apparatus for this purpose is strongly required to be capable of forming a film with good coatability over the entire to-be-processed substrate accompanied by the recent trend for micro-fine wiring patterns with respect to micro-holes (micro-pores) of high aspect ratio, i.e., an improvement in coverage is strongly required.
In the conventional sputtering apparatus, there is disposed a magnet assembly provided with a plurality of magnets behind a target (i.e., on the side lying opposite to the surface to be sputtered) while alternately changing the polarities. By means of this magnet assembly, a tunnel-like magnetic field is generated in front of the target (i.e., on that side of the target which is sputtered). The electrons that are ionized in front of the target and the secondary electrons generated by the sputtering are collected by the magnetic field to thereby increase the electron density in front of the target, whereby the plasma density is increased.
In the above-mentioned kind of sputtering apparatus, those regions of the entire target which are subjected to the influence of the above-mentioned magnetic field are preferentially sputtered. Therefore, in case the above-mentioned regions are located, e.g., near the center of the target from the viewpoint of stability in electric discharging or of the improvement of the use efficiency of the target, the amount of erosion of the target at the time of sputtering increases near the center of the target. Therefore, in the peripheral portion of the substrate, the target material particles (e.g., metallic particles, hereinafter referred to as “sputtered particles”) are incident and get adhered at an inclined angle. As a result, in case the sputtering apparatus is used for film forming of the above-mentioned purposes, it is known that there will arise a problem of asymmetry of coverage especially in the peripheral portion of the substrate.
In order to solve the above problems, there is known, in Patent Document 1, a sputtering apparatus in which: a first target is disposed above a stage on which the substrate is mounted inside the vacuum chamber, the first target being substantially in parallel with the surface of the stage; and a second target is disposed slantingly above the stage at an inclination relative to the surface of the stage, i.e., a sputtering apparatus in which a plurality of cathode units are disposed.
However, if a plurality of cathode units are disposed in the vacuum chamber as in the above-mentioned Patent Document 1, there is a disadvantage in that the apparatus arrangement becomes complicated, and that a higher cost will be incurred due to an increase in the number of parts because power supplies for activating power as well as magnet assemblies are required corresponding to the number of targets.
On the other hand, the inventors of this patent application developed a cathode unit which has a bottomed cylindrical target material (i.e., a target material of a cylindrical shape having a bottom such as a cup) to be mounted from a bottom side thereof into a recessed portion formed in one surface of a holder so that a magnetic field can be generated in an inside space of the target material. Then, they came to a finding that, by applying this cathode unit to a sputtering apparatus in which a vertical magnetic field works over the entire surface of the substrate, film forming can be performed while keeping an extremely high uniformity in film thickness in a portion lying opposite to an opening in the target material and therearound (Japanese Patent Application No. 2008-167175).
When a barrier film of Cu or Ta is formed relative to micro-holes by using the above-mentioned arrangement, if film forming by sputtering is performed by self-discharging in the inside space of the target material, the following disadvantage has been found to take place, i.e., that the upper openings of the micro-holes will be clogged by getting covered with a thin film made up of the sputtered particles.